The present invention relates to a method of surface hardening stainless steel parts for increasing their wear and fatigue resistance.
Nitriding surface hardening processes are commonly used for increasing wear and fatigue resistance of steel parts. Either of the two conventional nitriding processes, namely gas nitriding and salt-bath nitriding, can be performed without difficulty on parts made of alloy steels. However, the nitriding of stainless steel (austenitic, martensitic and precipitation hardening) presents difficulties because of the presence of a passive oxide film on the surface of the stainless steel part which inhibits nitriding. Special procedures have therefore been developed for nitriding stainless steel parts, including one known as "Malcomizing" in which chemical pills are added to the retort during the nitriding process, the decomposition of the pills causing depassivation of the protective oxide film, and another known as "Ionitriding," in which the nitriding takes place in the plasma of a current-intensive glow discharge. Such procedures, however, involve the use of expensive ingredients and/or expensive equipment.